1. Field of the Invention
The present invention relates to a fiber construction suitable for various industrial uses. More particularly, the present invention relates to a fiber construction of a high tenacity as well as a high softness, which is capable of being melt spun, as well as woven, without accompanying operational difficulties such as generation of naps or filament breakages. Further, more particularly, the present invention relates to a fiber construction of reduced air permeability, which is practically useful as a basic fabric for an air bag and the like.
2. Description of Related Art
A fiber construction made of synthetic fibers is widely used for various field in materials for industries: such as rubber reinforcing materials for items such as tires, belts such as V-belts or conveyor belts, and hoses; woven or knitted fabrics such as a canvas, tent, tarpaulin, cover sheet, seat belt, and air bag fabrics; fish nets; ropes; and sewing threads.
It has heretofore been known that a thread used for producing the fiber construction for the above items must have a fineness of a single filament of 5 denier or more. Such a limitation of a fineness of the single filament is derived, on one hand, from requirements as to thread performance, such as, obtaining a high-strength of a thread, and reducing the specific surface area to prevent the fiber construction from being degraded at its surface and, on the other hand, from a productivity requirement such as preventing operational difficulties, such as naps and filament breakage, from increasing during a melt spinning process.
However, due to the recent industrial use of a fiber construction in various textile related products, such as canvas, tent, tarpaulin, and air bag fabrics, it has been frequently required that the fiber construction provides a high-strength, reduced weight and increased softness.
In order to meet the above-mentioned requirements in various field of use, various improvements have been attempted including, for example, reducing the total denier of the filaments, or the denier of a single filament, in the fabric, have been proposed.
When an application to a basic fabric for an air bag is considered, a first requirement is that the air bag has a low value of air permeability as well as a high mechanical strength, which allows the bag to be quickly expanded when a shock is generated. Additionally, it is also requested that a driver or a passenger is prevented from being abrasively wounded especially on his or her face when the air bag is inflated, that the air bag is in a compact condition when it is stored, and that any substantial dimensional change does not occur during a prolonged storage in an automobile body.
It is, however, difficult to meet all of the above requirements. For example, when a basic fabric for an air bag is produced so as to cause, among these requirements, the one for reducing the air permeability to be met, the basic fabric becomes too thick, which causes the fabric to be lacking in a compactness in a folded state, on one hand, and the impact force to be increased upon the contact between the air bag and a human body, thereby causing a driver or passenger to be abrasively wounded upon the inflation of the air bag. In short, a construction of the basic fabric for the air bag must be such that a plurality of requirements, which contradict each other, are met.
Various basic fabrics have heretofore proposed for utilization in an air bag. For example, Japanese Un-Examined Patent Publication No. 3-243442 proposes a basic fabric made of nylon yarns with no coating, with a single filament denier of 4 to 7 and with a total denier of 400 to 1,000 (below; non-coated type), as well as a basic fabric of the same construction with a coating of resin such as chloroprene or silicon (below; coated type).
Irrespective of an advantage of a low gas permeability, this type of basic fabric for an air bag is defective in that large value of the total denier of the filaments constructing the yarn as well as a large value of a denier of the single filament make the fabric to be lacking in softness, thereby causing its compactness to be worsened, on one hand, and an impact force to be increased upon contact of the inflated air bag with a human body, on the other hand. Furthermore, as far as the coated basic fabric is concerned, a process for producing the same is complicated and it is difficult to obtain a uniform thickness of the coating of the resin on the surface of the basic fabric.
In order to obviate the above-mentioned drawbacks, various improvements have been proposed. For example, Japanese Un-Examined Patent Publication No. 1-104848 proposes to provide a basic fabric made of multi-filament yarn with a reduced value of the total denier, in order to reduce the thickness of the fabric, thereby making the obtained basic fabric to be more soft, on one hand, and the fabric to be more compact in a folded state, on the other hand.
However, only a reduction in the value of the total denier causes the gas permeability to be excessively increased, which causes the coating by the resin to be inevitable, which makes the compactness of the basic fabric to be worsened. In order to obtain both of the low gas permeability and an improved compactness, a method is conceivable that the total denier is reduced, while increasing the density of woven fabric. However, the usual range of the denier of the single filament between 4 and 7 (d) provides a limitation in an improvement in the softness of the fabric by the reduction of the value of the total denier, which makes it difficult to improve the softness to a desired value.
Furthermore, in order to obtain a neatly foldable structure in the coated type product, the Japanese Unexamined Patent Publication No. 64-41438 has proposed a basic fabric for an air bag, wherein it is produced from a multi-filament yarn of a tenacity of 8.5 g/d or more and of a denier of a single filament of 3 (d) or less. Furthermore, the Japanese Patent Publication No. 4-214437 proposes a non-coated type of basic fabric for an air bag made of polyethylene terephthalate multi-filament yarns with a denier of a single filament of 4 dtex or less and of a total denier in a range between 250 to 400 dtex.
However, in these prior art, as described in the disclosed embodiment, the reduction of a value of the denier of a single filament is, at best, limited to about 2 denier. As a result, only a partial improvement in the basic fabric as to the softness as well as neatness when folded can be obtained, which does not meet the above-mentioned various requirements for the basic fabric for an air bag. Furthermore, the yarns in these publications are obtained by a direct spinning method as disclosed therein. Such a direct spinning method is defective in that the finer the denier of the single filament, the more frequent the occurrence of naps and breakage of single filaments during a spinning process as well as a weaving process. In addition, the weaving process of a fabric for an industrial use such as a basic fabric for an air bag is usually done by using non-twisted yarns in a non-sized condition, which makes it easy for the yarns to generate naps as well as for the single filaments to break. Furthermore, in the case of an extremely fine yarn with a fineness of a single filament of 1.0 denier or less, even if no nap is generated in the yarns during the preceding spinning and winding process, the following weaving process may easily cause the yarns to produce naps and to break. As a result, it is considered that the prior art methods disclosed in the above-mentioned publications make it difficult to produce, in industry, a basic fabric for an air bag from the ultra-fine yarns with a denier of the single filament smaller than 0.8 (d), from the view points of reduced operational performance during the spinning process (a low spinnability) as well as weaving process (a low weavability).
Furthermore, Japanese Un-Examined Patent Publication No. 1-122752 discloses a method wherein a high density woven fabric is subjected to a shrinkage process, which is followed by a thermal fixing process and then by a calendering process, to obtain a basic fabric for an air bag with a high dimensional stability. However, since, in this prior art, the thread used in the prior art has a single filament denier of 1 (d) or more, the calendering process is insufficient to improve the softness to a desired level.
As a further prior art, Japanese Un-Examined No. 4-2835 discloses a non-coated type of basic fabric for an air bag made from a polyethylene terephthalate of low weight and a small thickness, which features that the air permeability is 0.5 cc/sec/cm.sup.2 or less, the elongation at break is 650 psi or more, the tenacity is 300 lb or more, and the tearing strength of trapezoidal shaped test piece is 40 lb or more. In this prior art, the fineness of a single fiber is, at best, limited to about 1 denier, and the above-mentioned calendering process is essential for suppressing the gas permeability, so that the above-mentioned problems have remained unsolved.
In still further prior art, a use of ultra-fine fibers with a fineness of 1 denier or less has been proposed for use in clothes, as disclosed in Japanese Un-Examined Patent Publication No. 5-213131. However, the ultra-fine fibers used for the clothes in the prior art are produced using a polymer of an intrinsic viscosity of a value in a range between about 0.6 to 0.7, so that the tenacity of the yarn is as low as a value in a range between 2.5 to 4.5 g/denier, which makes it difficult to obtain an air bag of a desired strength. In view of this, it has also been proposed to combine the ultra-fine yarns with conventional yarn of a high tenacity and usual fineness, thereby preventing the tenacity from being lacked. Such a solution of combining the yarns causes, however, the advantage using the ultra-fine fibers, i.e., the high softness, to be lost.
As stated above, attempts have not been made in the prior art to produce and use an ultra-fine fiber using a 0.8 denier or less single filament, while maintaining a desired high tenacity.
As far as a use of ultra-fine fibers is concerned, Japanese Un-Examined Utility Model No. 56-56500 proposes to use such an ultra-fine fiber for an extendable fabric for a parachute. However, in this publication, the degree of the fineness of the single fiber is only mentioned, and no mention is made of the tenacity. In other words, nothing is mentioned in this prior art as to ultra-fine fibers capable of providing a high tenacity.
In short, there has been long felt a need, not yet realized, to produce a fiber construction for an industrial use, capable of providing a desired mechanical strength and softness, as well as a low air permeability, if it is needed, while suppressing the occurrence of naps as well as maintaining a desired quality.